Process and apparatus for analyzing gas



Jan; 10, 1939. L L. VAYDA {IT-AL 2,143,041

PROCESS AND APPARATUS FOR ANALYZING GAS Filed April 26, 1934 INVENTORS ATTORNEY Patented Jan. 10, 1939 PROCESS AND APPARATUS FOR ANALYZING GASLouis L. Vayda, Aspinwall, and Joseph A. Stein, Pittsburgh, Pa.

Application April 26, 1934, Serial No. 722,490

7 Claims.

The invention relates to a process and apparatus for analyzing gas. Theobjects of the invention are the provision of a process and apparatuswhich have a very wide field of use permitting their use for practicallyall gases for which commercial requirement for analyzing exists. Afurther object is the provision of an apparatus which is dependable andaccurate; which is operable without difficulty; and which is relativelycheap! and simple in construction.

The process involves the use of a closed system, to which a gas mixturecontaining a constituent or constituents, whose percentage is to bedetermined, is supplied continuously, such mixture also containing a gasor gases which will react with said constituent or constituents. Thisreaction is caused to occur by the application of a suitable degree ofheat and/or by a catalyzing agent, and a residual volume of gas isconstantly evacuated from the system. If the volume of gases in thesystem tends to be increased or reduced by the reaction, this will beindicated by a change in pressure in the system, and it is thisVariation in pressure which indicates the extent of the reaction andconsequently the amount of the reacting constituent. The instrument usedmay be easily calibrated to indicate the percentage of the constituentin the gas being tested. This will be readily understood from aconsideration of the apparatus of the drawing, wherein:

Figure 1 is a diagrammatic view partly in section showing the movingparts in one position. Fig. 2 isa similar view of a part of theapparatus with the moving parts in another position. And Fig. 3illustrates a modification.

Referring to the drawing, i and 2 are a pair of cylinders mounted forreciprocation, and provided with the ports 3, 4, 5 and 6; and l and 8are a pair of pistons working in the cylinders 40 and provided withpiston rods 9 and Ill connected to the common cross head I I. This crosshead is slidable in the block Ha and is driven from the electric motorl2 by means of the crank l3 and connecting rod M. A gas to be analyzedfor CO+H2 content, such as flue or exhaust gases from the combustion offuel, is supplied to the cylinder I through the pipe 15, while a secondgas, such as air, is supplied to the cylinder 2 through the pipe I6. Thetwocylinders discharge to a closed system which includes the pipes l1,l8 and i9, and the furnace 20 through the passage 2| when the parts arein the position of Fig. 1 with the ports 3 and 5 in registration withsuch passage. The furnace 2!! is heated from the coil 22 supplied withelectric current from the leads 23 and 24, which also supply current fordriving the motor l2. The pipes i8 and I9 are connected to the pressureindicators 25 and 2B, the latter of which is of the recording type. Thepipe 18 is connected by means of a pipe 21 with a passage 28 whichcommunicates at its ends with the ports l and 6 when the parts are inthe position of Fig. 1. 29 is an exhaust passage to the atmosphere whichregisters with the ports 4 and 5 when the parts are in the position ofFig. 2. The cylinders l and 2 are mounted for sliding movement from oneextreme position, as indicated in Fig. 1, to another extreme position,as indicated in Fig. 2, and their movement from one position to theother occurs when the pistons l and 8 approach the ends of their strokesand engage the cylinder heads. The cylinders are pressed yieldinglyagainst the surfaces upon which they slide by any suitable means which,in the present case, are diagrammatically shown as plates 30 and 3|engaging the outer faces of the cylinders and pressed inward by springs32 and 33.

Starting with the parts in the position of Fig. 1, and the pistonsmoving to the right, the pistons are forcing into the pipe H the gasesin the cylinders to the right thereof via the ports 3 and 5 and passage2|. At the same time, gas is being evacuated from the pipe 2? into thecylinders to the left of the pistons via the passage 28 and ports 4 and6. This causes a circulation of the gas through the pipe ll, furnace 2B,and pipe [8, giving opportunity for a reaction to occur in the furnaceresulting in a change in pressure, as more fully described later.

This supply of gas to the pipe ll and withdrawal through the pipe 21continues until the pistons reach the right hand ends of the cylinderswhere they engage the cylinder heads, and move the cylinders to theposition of Fig. 2. This brings the ports 3 and 5 into registration withthe passages 34 and 35 respectively with which the pipes l5 and I6communicate, and as the pistons move to the left, the cylinders arecharged with gas from such pipes. With the cylinders in the position ofFig. 2', the ports 4 and 6 are in registration with the exhaust passage29 so that, as the pistons move to the left, the contents of thecylinders to the left of the pistons is discharged to the atmosphere.This charging of the right hand ends of the cylinders and the exhaustingof the left hand ends thereof continues until the pistons engage theheads at the left hand end of the cylinders, when such cylinders areshifted to the left to the position of Fig. 1. The pistons now start tothe right, bringing the parts back to the starting point of the cycle asabove outlined.

In the above operation, the reactions in the furnace 20 transforming theCO in the fiue gases to CO2 and the hydrogen to H2O would normallyreduce the volume of the gases of reaction, as compared with the initialvolume of the gases mixed. It follows that since the capacity of thesystem remains constant, the pressure will be reduced in proportion tothe extent of the reaction, so that by proper calibration of theindicators 25 and 26, these can be made to read in terms of thepercentage of the combustible constitnent supplied from the pipe I5.

The reaction which occurs in the reactions above indicated is shown bythe following equations:

2H2+O2=2H2O From which it is seen that three volumes of the reactinggases in either case give two volumes of gaseous products of reaction.This operation, in order to give accurate results, will require that thecylinders connecting passages and piping be maintained at a temperaturehigh enough to prevent condensation of the water vapor formed by thereacting gases, which can easily be accomplished by placing theapparatus in a heated cabinet (not shown) or by submerging it in aheated liquid, such as oil, which latter expedient has the furtheradvantage of lubricating the moving parts.

A further application of the apparatus is in the determination of thepercentage of oxygen in the flue and furnace gases from boiler furnaces,industrial heating and annealing furnaces, open hearth furnaces, kilns,etc. In using the apparatus, the cylinder I is connected to draw in thegas to be analyzed, while the cylinder 2 is connected to draw in a gaswhich will unite with the oxygen, such as hydrogen. The reaction in thefurace is indicated by the following equation:

From which it is seen that three volumes of the reacting gases give twovolumes of the gaseous products of the reaction, resulting in a changein pressure in the system as heretofore described. This use of theapparatus also requires a maintenance of the temperature of theapparatus above a given point to prevent condensation, and suitablemeans may be employed for this purpose as above pointed out.

The apparatus may further be used to determine the per cent of carbonmonoxide and/or hydrogen in air, such as may exist in vehicular tunnels,garages, or other confined spaces subject to pollution by the exhaustgases from automotive vehicles: In this case, however, the air to betested is drawn into the system from the pipes 15 and 16 by both pistonsl and 8, the oxygen in the mixture being suiiicient to give thenecessary reaction in the furnace 25. The reaction is indicated in thefollowing equation:

It will be seen that three volumes of the reacting gases in either casegives two volumes of gaseous products of reaction. But since thepercentage by volume of carbon monoxide and/or hydrogen in the airtested, will in most cases be small, the volume change due to thereaction, will be correspondingly small, perhaps too small for practicalmeasurement of the resulting change in pressure. It is, therefore,desirable to increase the difference in pressure, and this isaccomplished by bringing into play the condenser or absorber unit 34,connected to the pipe l8 by pipes and 36 provided with the valves 31 and38. The unit may be equipped to provide for the removal of the carbondioxide formed, as by the use of potassium hydroxide and/or for theremoval of the water vapor by the use of calcium chloride. When so used,the gases from the furnace, are caused to pass through the casing 34 byclosing the valve 33'- and opening the valves 31 and 38. The volume ofthe reacting gases may, in this manner, be removed from the system, andthe resulting change in pressure is correspondingly increased. When theuse of the unit 34 is not required, it is cut off from the system by thevalves 3'! and 38, at which time the valve 39 is open.

The apparatus may be similarly employed to i determine the percentage ofinflammable gas or vapors in air, such as for example the percentage ofmethane in air which has been used for the ventilation of a mine. As inthe Preceding example, the gas to be tested is drawn in through thepipes l5 and i6 by both pistons, and the unit 34 is utilized. In thiscase, the reaction is indicated by the following equation:

It will be seen that three volumes of the reacting gases gives threevolumes of the gaseous products of the reaction. There is thus no changein volume, and no change in pressure. The necessary change in pressureis secured by passing the gases through the unit 34, which, as before,is equipped to chemically remove the carbon dioxide, as by the use ofpotassium hydroxide, and to remove the water vapor by the use of calciumchloride. The volume of reacting gases may thus be removed and theresulting variation in pressure in the system measured.

Fig. 3 illustrates a modified means for holding the cylinders againsttheir seats and maintaining them yieldingly in their extremes ofmovement until positively moved by the pistons. cylinder is provided onits upper side with two recesses 4|] and 4| adapted to be engaged by theroller 42 on the arm 43 yieldingly pressed down by the spring 44, thearm 43 being pivoted to the fixed bracket 45. The cylinder is held inthe position shown until the piston which is moving to the left engagesthe end of the cylinder and moves it to the left. The roller 42 resiststhis movement, but is cammed upward and then moves down and engages therecess 4| holding the cylinder in its new position until the reversemovement of the piston shifts the cylinder back to the position shown.

It will be understood that the apparatus is illustrated in a very simpleform and is capable of various modifications. Other forms of pumps maybe substituted for those shown, such as those of the rotary displacementtype. In some cases, the apparatus may be made with only the one pumpfor use in those cases in which no additional gas need be applied to thesystem to promote the reaction as in the determination of CH4 in air asheretofore described. It is also not necessary to provide for thereaction by heat as supplied in T the furnace 20. The reaction may besecured by the use of a catalyzing agent with or without heat, such asmay be accomplished by the use of palladium sponge or certain metallicoxides.

What we claim is:

The

1. An apparatus for analyzing gas, comprising a closed reaction systemprovided with a pressure indicator, and means for delivering a gasmixture into the system and evacuating it therefrom comprising a pistonand means for reciprocating it, a cylinder in which the piston worksmounted for limited endwise movement, and adapted to be moved endwise bythe piston when it reaches the end of its stroke in each direction, aport at one end of the cylinder through which the gas to be analyzed issupplied when the cylinder is in one position and the piston isretreating from the port and through which the gas is expelled into thesystem when the cylinder is in its other position and the piston ismoving toward the port, and a second port at the other end of thecylinder through which the gas to be evacuated from the system issupplied from the system when the cylinder is in its last mentionedposition and the piston is retreating from the said second port andthrough which gas is expelled to the atmosphere when the cylinder is inits first mentioned position and the piston is moving toward the saidsecond port.

2. A method of analyzing gas, which consists in separately pumping intoa closed gas tight system (1) a gas mixture containing a constituent thepercentage of which it is desired to determine, and (2) a fixedproportion of some other gas which will react with the constituent in adefinite manner so that the volume of the gaseous products of thereaction tends to vary from the initial volume of the combining gases,causing said reaction to occur, treating the products of said reactionto reduce their volume, withdrawing from the system by a pumpingoperation coincident with the supply of gas thereto a quantity of thegas which has been exposed to said reaction bearing a fixed relation tothe quantity of gas delivered into the system, and measuring thevariation of pressure in the system while gas is being supplied to thesystem and withdrawn therefrom.

3. An apparatus for analyzing gas, comprising a closed gas tight passageprovided with an inlet and an outlet, a pressure indicator connected tothe passage, two sets of pumping means each of which is connected tosaid inlet and outlet, one of which is adapted to supply a gas to betested and the other of which to supply a reaction gas to said inlet,and which pumping means simultaneously withdraw a volume of gas fromsaid outlet which is equal to the volume supplied to the inlet, ignitionmeans in the passage past which the gas is caused to flow by the pumpingmeans, and means for driving the pumping means continuously.

4. A method of analyzing gas, which consists in pumping continually intoa closed gas tight system, a gas mixture containing a constituent whosepercentage it is desired to determine, said mixture containing someother gas which will react with said constituent in a definite manner sothat the volume of the gaseous products of the reaction tends to varyfrom the initial volume of the combining gases, causing said reaction tooccur, withdrawing continually from the system coincident with thesupply of gas thereto, and by a pumping operation a quantity of gaswhich has been exposed to said reaction bearing a fixed relation to thequantity of gas delivered into the system, and measuring the variationin pressure in the system while the operations of supplying gas to thesystem and withdrawing it therefrom are in progress.

5. A method of analyzing gas, which consists in pumping continually intoa closed gas tight system a gas mixture containing a constituent whosepercentage it is desired to determine, said mixture containing someother gas which will react with said constituent in a definite manner sothat the volume of the gaseous products of the reaction tends to varyfrom the initial volume of the combining gases, causing said reaction tooccur, withdrawing continually from the system coincident with thesupply of gas thereto and by a pumping operation a quantity of gas whichhas been exposed to said reaction which is equal to the quantity of gasdelivered into the system, and measuring the variation in pressure inthe system: while the operations of supplying gas to the system andwithdrawing it therefrom are in progress.

6. An apparatus for analyzing gas, comprising a closed gas tight passageprovided with an inlet and an outlet, a pressure indicator connected tothe passage, pumping means connected to said inlet and outlet andadapted to simultaneously supply a volume of gas to be tested to saidinlet and to withdraw a volume of gas from said outlet bearing a fixedrelation to the first volume of gas, ignition means in the passage pastwhich the gas is caused to flow by the pumping means, and means fordriving the pumping means continuously so as to cause a continual flowof gas past the ignition means.

'7. An apparatus for analyzing gas, comprising a closed gas tightpassage provided with an inlet and an outlet, a pressure indicatorconnected to the passage, pumping means connected to said inlet andoutlet and adapted to simultaneously supply a volume of gas to be testedto said inlet and to withdraw a volume of gas from said outlet bearing afixed relation to the first volume of gas, ignition means in thepassage, absorption means in the passage between the ignition means andsaid outlet for absorbing a part of the products of the reaction whichoccurs due to the ignition means, and means for driving the pumpingmeans continuously so as to cause a continual flow of gas past theignition and absorption means.

LOUIS L. VAYDA. JOSEPH A. STEIN.

